The delivery of drugs through the skin provides many advantages; primarily, such a means of delivery is a comfortable, convenient and noninvasive way of administering drugs. The variable rates of absorption and metabolism encountered in oral treatment are avoided, and other inherent inconveniences--e.g., gastrointestinal irritation and the like--are eliminated as well. Transdermal drug delivery also makes possible a high degree of control over blood concentrations of any particular drug.
Skin is a structurally complex, relatively thick membrane. Molecules moving from the environment into and through intact skin must first penetrate the stratum corneum and any material on its surface. They must then penetrate the viable epidermis, the papillary dermis, and the capillary walls into the blood stream or lymph channels. To be so absorbed, molecules must overcome a different resistance to penetration in each type of tissue. Transport across the skin membrane is thus a complex phenomenon. However, it is the cells of the stratum corneum which present the primary barrier to absorption of topical compositions or transdermally administered drugs. The stratum corneum is a thin layer of dense, highly keratinized cells approximately 10-15 microns thick over most of the body. It is believed to be the high degree of keratinization within these cells as well as their dense packing which creates in most cases a substantially impermeable barrier to drug penetration.
In order to increase skin permeability, and in particular to increase the permeability of the stratum corneum (i.e., so as to achieve enhanced penetration, through the skin, of the drug to be administered transdermally), the skin may be pretreated with a penetration enhancing agent (or "permeation enhancer", as sometimes referred to herein) prior to application of a drug. Alternatively, and preferably, a drug and a permeation enhancer are concurrently delivered.
The present invention is directed to a novel method and composition for enhancing the penetration of a drug through skin. The invention is premised on the discovery that certain vegetable oils used individually or in combination are effective in enhancing the penetration of pharmacologically active agents through the skin.
While there are a number of patents and publications which relate to the use of a variety of different skin permeation enhancers, applicants are unaware of any art which relates to the use of vegetable oils as disclosed herein as skin permeation enhancers.
The following references relate generally to the use of permeation enhancers in transdermal formulations. U.S. Pat. Nos. 4,006,218, 3,551,554 and 3,472,931, for example, respectively describe the use of dimethylsulfoxide (DMSO), dimethyl formamide (DMF) and N,N-dimethylacetamide (DMA) to enhance the absorption of pharmacologically active agents through the stratum corneum. Other compounds which have been used to enhance skin permeability include: decylmethylsulfoxide (C.sub.10 MSO); Transcutol, cited in the preceding section; polyethylene glycol monolaurate (PEGML); (see, e.g., U.S. Pat. No. 4,568,343); glycerol monolaurate (U.S. Pat. No. 4,746,515); propylene glycol monolaurate (see European Patent Application No. 87402945.7, Published as EP Publication No. 272 987, which derives from U.S. patent application Ser. No. 945,356, filed 22 Dec. 1986, of common assignment herewith); ethanol (e.g., as in U.S. Pat. No. 4,379,454); eucalyptol (U.S. Pat. No. 4,440,777); lecithin (U.S. Pat. No. 4,783,450); the 1-substituted azacycloheptan-2-ones, particularly 1-n-dodecylcyclazacycloheptan-2-one (available under the trademark Azone.RTM. from Nelson Research & Development Co., Irvine, Calif.; see U.S. Pat. Nos. 3,989,816, 4,316,893, 4,405,616 and 4,557,934); propylene glycol in combination with a fatty acid such as linoleic acid (European Patent Publication No. 261429); "cell envelope disordering compounds" such as methyl laurate or oleic acid in combination with N-(hydroxyethyl) pyrrolidone (U.S. Pat. No. 4,537,776) or C.sub.3 -C.sub.4 diols (U.S. Pat. No. 4,552,872, European Patent Application Publication No. 043738). U.S. Pat. No. 4,764,379 discloses a binary enhancer composition of ethanol and glycerol monolaurate.